1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display (LCD) apparatus, and more particularly, a method for manufacturing the drain/source electrodes of a thin film transistor (TFT).
2. Description of the Related Art
Active matrix-type LCD apparatuses are so thin and light that they are often used in various display apparatuses. Also, since the active matrix-type LCD apparatuses can be of a large size and fine screen with a high quality and a low power dissipation, cathode ray tubes (CRTs) have been replaced with the active matrix-type LCD apparatuses.
In an active matrix-type LCD apparatus, one TFT is provided as a switching element for each pixel. The TFT is constructed by a gate electrode, a semiconductor active layer made of amorphous silicon opposing the gate electrode, a drain electrode, and a source electrode connected to a transparent pixel electrode.
In a prior art method for manufacturing an LCD apparatus, a gate electrode is formed, on an insulating substrate, and a gate insulating layer is formed on the gate electrode. Then, a semiconductor active layer made of amorphous silicon is formed on the gate insulating layer. Then, a metal layer is formed on the semiconductor active layer. Thereafter, in order to obtain good ohmic contact between the metal layer and the semiconductor active layer a metal silicide layer is formed by reacting the metal layer with the semiconductor active layer by using a ramp annealing operation or the like at about 250 to 300.degree. C. Then, the metal layer is etched by a dry etching process to form drain/source electrodes. Finally, the semiconductor active layer is etched by a dry etching process using the drain/source electrodes as a mask. This will be explained later in detail.
In the above-mentioned prior art method, however, since the metal silicide layer is too thin (about 5 to 10 nm), the overetching of the metal layer invites etching of the semiconductor active layer. Note that the etched amount of the semiconductor active layer is not reproducible due to the etching selection ratio of the metal layer to the semiconductor active layer produced by the dry etching being about 1. As a result, the characteristics of the TFT are deteriorated, which creates the display distortion.
In addition, since the metal silicide layer is not present between the signal bus line and the gate insulating layer, electromigration is easily generated in the part of the signal line bus above the scan bus line. Particularly, this electromigration is fatal in a large scale LCD apparatus which is easily warped.